Terephthalic acid is an inexpensive chemical that is produced in large quantity mainly as a raw material of terephthalic acid-based polyesters including polyethylene terephthalate (hereinafter abbreviated as PET), polytrimethylene terephthalate (hereinafter abbreviated as PTT), and polybutylene terephthalate (hereinafter abbreviated as PBT). Because terephthalic acid is inexpensive, technologies of producing useful chemicals such as TPA-DHD, 2-pyrone-4,6-dicarboxylic acid, protocatechuic acid, or gallic acid with terephthalic acid as a raw material using microorganisms have been developed (Documents 1 to 5). It has been known that 2-hydroxy terephthalic acid which is a raw material of pharmaceutical products or resin materials can be produced by a dehydration reaction of TPA-DHD (Patent Documents 1 and 2).
In cases where useful chemicals are produced with terephthalic acid as a raw material using microorganisms, it is desired to add terephthalic acid salt which are excellent in water-solubility, rather than terephthalic acid per se, to a culture medium. Because sodium hydroxide is less expensive than potassium hydroxide, sodium salts of terephthalic acid has been thus far used as the raw material. There are no reports describing production of useful chemicals with potassium salts of terephthalic acid as raw materials using microorganisms or no reports showing that the capacity of the sodium salt of terephthalic acid in production of an intended compound is superior to that of the potassium salt of terephthalic acid.
With regard to recycling of terephthalic acid-based polyesters, a number of recycling technologies have been developed in particular with focus on the recycling of waste PET bottles and are advancing toward commercialization. However, the cost for the recycling is high, and a more profitable recycling technology is demanded. As seen above, the use of terephthalic acid derived from waste polyesters as raw materials in the production of chemicals leads to solution for environment problems and to reduction of the production cost, and is therefore an important research and development issue.
As a method of recycling waste polyesters, in addition to a material recycling method whereby original polyesters are obtained, a chemical recycling method whereby terephthalic acid, bis-2-hydroxyethyl terephthalate, or the like is obtained through chemical depolymerization of polyesters is known (Patent Documents 6 to 11). It has been known that depolymerization is feasible by heating polyesters such as PET in an ethylene glycol reaction solvent or alcohol reaction solvent containing an alkali metal hydroxide such as sodium hydroxide. In this case, because sodium hydroxide is inexpensive, sodium hydroxide is in general used as the alkali metal hydroxide. Yet, because there are no usage applications of the obtained alkali metal terephthalate, it is anticipated to set forward recycling operation of further subjecting the alkali metal terephthalate to acid treatment to obtain terephthalic acid. However, such a recycling operation is hardly carried out because the production cost tends to be high and the obtained terephthalic acid is inexpensive.
Although it has been known that PET can be depolymerized in an ethylene glycol solvent containing potassium hydroxide (Non-patent Document 1), there are no reports on results of comparing difference in PET depolymerization between potassium hydroxide and sodium hydroxide in the ethylene glycol solvent. Further, there are no reports on technologies of recycling waste polyesters wherein, after PET, PTT, or PBT is depolymerized in an ethylene glycol reaction solvent containing potassium hydroxide to thereby obtain potassium terephthalates, such potassium terephthalates are converted into other useful chemicals using microorganisms.
An example of an experiment has been reported, wherein terephthalic acid is obtained by depolymerizing waste PET in a 1-butanol reaction solvent containing sodium hydroxide and adding sulfuric acid (Patent Document 12). Yet, there are no reports where waste PET is depolymerized in the 1-butanol reaction solvent containing potassium hydroxide, and where difference in a reaction of depolymerizing polyester in the 1-butanol reaction solvent containing alkali is compared between potassium hydroxide and sodium hydroxide.
In cases where waste polyesters are depolymerized in ethylene glycol containing potassium hydroxide, if an attempt to obtain potassium terephthalate with high purity is made, the cost for the recycling increases. Thus, using potassium terephthalate with low purity containing ethylene glycol as a raw material, it is desired to convert into useful chemicals using microorganisms. However, there are no reports on production of chemicals using microorganisms in a condition where terephthalate and ethylene glycol are present together. It is to be noted that Escherichia coli (hereinafter, as appropriate referred to as Escherichia coli) K-12 strain which is often used in the field of basic research and the field of industrial production is known to be capable of converting ethylene glycol into glycolic acid by lactaldehyde reductase and lactaldehyde dehydrogenase thereof. Moreover, it has been reported that introduction of mutation into lactaldehyde reductase improves the ability to metabolize ethylene glycol (Non-patent Documents 2 to 4).